The long term objectives of the research are to improve understanding of the evolution and diversity of antibacterial resistance plasmids in globally dispersed populations of bacteria in order to improve understanding and control of the spread of antibacterial resistance genes. The specific aims are to determine and computer file EcoRI fragment size values for resistance plasmids selected by resistance phenotype or randomly from an extensive series of isolate collections, to detect in this data further copies of previously recognized stable plasmids and further delineate their distributions, to detect and delineate distribution of additional stable plasmids and estimate their diversity, to develop methods for detecting and analyzing lesser relatedness between plasmids, to survey resistance plasmid prevalence, diversity and identity in fecal E. coli from untreated and unhospitalized humans in different parts of the world, to adapt and apply to data on fragment sizes of may isolates on one plasmid available statistical programs to reconstruct the plasmid's phylogenetic tree, and to detect and establish fine detail of regions involved in recombinational events that are significant for the spread of antibacterial resistance genes in globally dispersed populations of bacteria.